The present invention relates to a process for the treatment of heavy products resulting from the manufacture of chlorohydrocarbons, and more particularly for the treatment of the heavy products resulting from the manufacture of 1,2-dichloroethane, trichloroethylene, perchloroethylene, trichloroethanes or carbon tetrachloride.
In the manufacture of chlorohydrocarbons, heavy products of poorly defined composition are formed which are generally referred to as "tars". These products, which consist mainly of high-boiling chlorohydrocarbons, are found in the stills of the distillation columns used for the separation and purification of the products. In general, they are removed by purging the contents of the stills, but this causes significant losses of utilisable chlorohydrocarbons.
Various techniques have been developed in an attempt to recover the utilisable chlorohydrocarbons present in the purges.
Thus, Belgian Pat. No. 746,200 corresponding to U.S. Pat. No. 3,634,200, filed on 19th proposed that, in the manufacture of 1,2-dichloroethane, the purges be sent from the stills of the 1,2-dichloroethane column into film evaporators in which a mixture of 1,2-dichloroethane and 1,1,2-trichloroethane is recovered as the top fraction and a mixture of heavy chlorinated products is recovered as the bottom fraction; the separation of the latter has no technical or economic advantage and it is burnt. This technique is very difficult to carry out in a continuously operating industrial installation. In fact, the running of a film evaporator is very difficult and the installation must frequently be stopped in order to clean off the deposits and crusts. Moreover, in order to prevent the bottom of the evaporator from becoming fouled too rapidly, it is necessary to restrict the degree of vaporisation to a low percentage, and this does not enable the utilisable products to be recovered in their entirety.
Furthermore, attempts have been made to carry out a steam distillation process. Such a process does indeed enable the recoverable light products to be recovered in the top fraction, but the heavy products remaining in the bottom fraction form an emulsion with the water and this emulsion remains stable even when it is subjected to centrifugation. Since the emulsion obtained, which cannot be burnt because of its high water content and cannot be recycled, cannot be discharged as such into the environment, it has not been possible to use the steam distillation process.